Pneumatically actuated fastener driving devices, such as nailers and staplers, have long been in use and are well known in the art. The use of such tools is advantageous because they can drive fasteners more rapidly and more precisely than can be accomplished manually. However, a disadvantage of such pneumatically actuated tools lies in the fact that they require the presence of a source of compressed air and long lengths of hose. Thus, a compressor must be provided at the job site. Furthermore, such tools are not normally suited for home use, since a source of compressed air is not normally present in the home.
Recently, there has been much interest in electrically powered nailers and staplers, requiring only a source of electrical energy. Electrical energy is always present at a construction site. Electrical energy is also readily available in the home, making such tools appropriate for the home market.
Prior art workers have devised many types of electro-mechanical fastener driving tools. For example, U.S. Pat. Nos. 4,042,036; 4,204,662; and 4,323,127 each teach an electro-mechanical impact tool wherein the driver is frictionally moved through a working stroke by means of two counter-rotating flywheels, each flywheel being provided by its own electric motor. U.S. Pat. No. 4,121,745 also teaches an electro-mechanical impact tool utilizing counter-rotating flywheels to frictionally move the driver through its working stroke. In this instance, however, one flywheel is directly driven by an electric motor, while the other flywheel is driven by the same electric motor through the agency of pulleys and an elastomeric belt or gear means.
U.S. Pat. Nos. 4,189,080 and 4,298,072 teach electro-mechanical fastener driving tools wherein the driver is moved through a working stroke by means of a single rotating, high-speed flywheel. The driver is engaged between the single flywheel and a support element. The preferred form of support element comprises a low inertia roller. Both patents teach, however, that other support means, such as a linear bearing or a Teflon block, could be used to accomplish the same purpose.
Electro-mechanical tools of the general class described above can be used to drive nails, staples or the like. For purposes of an exemplary showing, the present invention will be described in terms of its application to an electro-mechanical nailer. It will be understood by one skilled in the art, however, that the teaching of the present invention are equally applicable to electro-mechanical staple driving tools.
One of the many ways in which all such electro-mechanical fastener driving tools differ from their pneumatically actuated counterparts is the manner in which the driver is returned to its normal, unactuated position, having completed a working stroke. In a pneumatically actuated tool, the driver is most usually returned by compressed air, the driver being attached to a piston located in the main cylinder of the tool. In an electro-mechanical tool, on the other hand, alternate means must be provided to return the driver to its normal, unactuated position, having completed a work stroke. The driver return means most commonly used comprises one or more elastomeric cords affixed at one end to the upper end of the driver and at the other end to an anchoring means within the tool housing.
Such elastomeric return means are subject to permanent stretching. Permanent stretching of the elastomeric return means is the result of a number of factors, such as cyclic use, elevated temperatures within the tool, the surrounding atmosphere, the tendency of the elastomeric material to stretch or creep and aging of the material. Stretching of the elastomeric cord or cords can take place to the extent that the driver is not fully returned to its normal, unactuated position. This, in turn, can result in improper functioning of the electro-mechanical fastener driving tool. Traditionally, such electro-mechanical fastener driving tools have not been provided with take-up compensation means. As a result, when stretch of the elastomeric cord or cords has become too great for proper operation of the tool, it has hitherto been necessary to disassemble the tool and adjust or replace the elastomeric cord or cords.
The present invention is directed to a driver return assembly utilizing one or more elastomeric cords and provided with a spring-loaded tensioner to compensate for or take up stretch occurring in the elastomeric cords. This greatly increases the service life of the elastomeric cord or cords and improves the operation and reliability of the electro-mechanical fastener driving tool.